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Requirements and locations of files
To migrate a Courier mailbox to Thunderbird (on Windows XP) you need Courier installed, Thunderbird installed and a program called Courex (get the latest copy here Courexor see the attachments for this page).
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# (2) this entry is similar but never the same
Step 1
Before you can migrate you have to start Thunderbird at least once and if possible create the mailbox you want to migrate. Enter the pop and smtp-settings and finish the wizard. Running the account wizard make sure you you disable the Global Inbox check mark if you want to use multiple email accounts and for each account a separate inbox.
Migrating the address book
The address book won't be automatically transferred. You find the address book in C:\Program Files\Courier Email\Mailbox\Courex
To import it properly open Thunderbird, go to address book/tools/import. Choose the text file option in the next window. In the 'select address book file' window change the 'Files of type' to 'All Files'. Then choose 'Address.csv' .